A high speed differential transceiver is commonly used in Fibre channel, Gigabit Ethernet, Serial ATA interfaces and other high speed serial bus standards. A physical layout/pinout of the transceiver is set by the appropriate standard and cannot be changed. The standards identify specific pins for the high-speed differential signals (i.e., RX+, RX−, TX+, and TX−) and physical alignment to standard connectors. The standards conventionally prevent the high-speed differential signals from being physically routed over each other.
Referring to FIG. 1, pinouts of a connector 10 that are required by the given standard interface do not line up with the current pinouts of a particular high-speed transceiver 12. In order to connect the differential receive lines and differential transmit lines to the required connector 10, the high speed differential signals RX+, RX−, TX+ and TX− need to be crossed over each other, either in the high-speed transceiver 12 or on the printed circuit board 14 (shown at points 16 and 18). Since the signals RX+, RX−, TX+ and TX− are very high speed (i.e., 1.5 Gigabits/sec to 3 Gigabits/sec) the amount of noise coupling that can occur from the “crossing over” of the signals can cause large increases in noise, jitter and bit error rates.
Printed circuit board designers are aware of the problems that the cross-overs cause. Crossing the high speed signals RX+ with RX− (and TX+with TX−) causes a certain amount of noise to be cross-coupled between the signals thus compromising signal integrity. Therefore, a large amount of time, effort and money is spent to minimize the induced effects of the cross-overs. Despite the efforts, the presence of the cross-overs will still cause some noise to be coupled over. Consequently, a risk is incurred in meeting the jitter requirements and bit error rates (BER) while allowing the transceiver to function robustly. Redesigning the transceiver to un-cross the signals is commonly unacceptable due to the amount of time and capital resources required. The cost of a new design include complete characterization testing and creating completely separate product tracking and support requirements.